The present invention relates to high purity poly(3-aminopropylmethylsiloxanes) and a method for their preparation. More specifically, the present invention relates to more than 95% isomerically pure poly(3-aminopropylmethylsiloxane) fluids, both linear and cyclic, prepared by the base catalyzed detrimethylsilylation and polymerization of at least 95% isomerically pure 3-(3-aminopropyl)-1,1,1,3,5,5,5-heptamethyltrisiloxane. These poly(3-aminopropylmethylsiloxanes) have utility as intermediates for other derivative poly(organofunctionalsiloxanes) and in cosmetic, textile, and automotive applications, and as coatings and adhesives.
There is considerable prior art relating to the synthesis of poly(aminoalkylmethylsiloxanes). Generally, poly(aminoalkylmethylsiloxanes) have been produced by first preparing aminoalkylmethyldialkoxysilanes, followed by hydrolysis with or without an endblocking agent, such as a trimethylsilyl derivative, to form cyclic and linear poly(3-aminoalkylmethylsiloxanes). The isomeric purity of the poly(aminoalkylmethylsiloxane) fluids, prepared in the manner of the prior art, is dependent upon the isomeric purity of the aminoalkylmethyldialkoxysilane prepared in the first step of the synthesis. German Patent No. 2408480 describes the reaction of a silazane derivative from allylamine and an organohydrochlorosilane, in the presence of a proton acceptor to form an intermediate silazane which then undergoes a hydrosilylation reaction catalyzed by a platinum catalyst. Upon alcoholysis, the intermediate hydrosilylation product forms 3-aminopropylmethyldiethoxysilane in 70% overall yield. A molar excess of at least 50% of allylamine is used in this process. Identification of the beta-isomer in the product was not made. Japanese Patent No. 10017578 describes another method of synthesis by hydrosilylation of N,N-bis(trimethylsilyl)allylamine by methyldimethoxysilane. The product of that reaction is then heated with methanol to form 3-aminopropylmethyldimethoxysilane in at least 85% overall yield. The presence of the beta-isomer in the product was not made. Japanese Patent No. 11209384 describes the use of a rhodium:cyclooctadiene complex as a hydrosilylation catalyst for the addition of methyldiethoxysilane to allylamine to form 3-aminopropylmethyldiethoxysilane in 78% yield. 2-Aminopropylmethyldiethoxysilane is formed at very low levels in this process not exceeding 0.5%. U.S. Pat. No. 5,391,675 describes the formation of an aminopropylmethylsiloxy-containing polydimethylsiloxane by barium or strontium hydroxide catalyzed condensation of a silanol terminated polydimethylsiloxane with a 3-aminopropylalkoxysilane with elimination of an alcohol.
However, none of the prior art references disclose the high isomeric purity poly(3-aminopropylmethylsiloxanes) of the present invention. The poly(3-aminopropylmethylsiloxanes) of the present invention have improved utility as intermediates for producing other poly(organofunctionalsiloxanes), and in cosmetic, textile and automotive applications, and as coatings and adhesives.
The present invention provides near quantitative yields of greater than about 95% isomeric purity of poly(3-aminopropylmethylsiloxanes) of the general formulae
Me3SiO(H2NCH2CH2CH2MeSiO)xSiMe3
(H2NCH2CH2CH2MeSiO)y
wherein Me is methyl, x may range from 2 to about 100 or more and y may range from 3 to about 7.
The present invention also provides a simple method for rapidly producing poly(3-aminopropylmethylsiloxanes) of the general formulae:
Me3SiO(H2NCH2CH2CH2MeSiO)xSiMe3
(H2NCH2CH2CH2MeSiO)y
wherein Me is methyl, x may range from 2 to about 100 or more and y may range from 3 to about 7, the method comprising heating of 3-(3-aminopropyl)-1,1,1,3,5,5,5-heptamethyltrisiloxane, of at least 95% isomeric purity, with a basic catalyst, and removing hexamethyldisiloxane.
The present invention provides near quantitative yields of greater than about 95% isomeric purity of poly(3-aminopropylmethylsiloxanes) of the general formulae:
Me3SiO(H2NCH2CH2CH2MeSiO)xSiMe3
(H2NCH2CH2CH2MeSiO)y
wherein Me is methyl, x may range from 2 to about 100 or more and y may range from 3 to about 7. The present invention also provides high purity poly(3-aminopropylmethylsiloxane) homopolymers which are greater than about 97% free of hexamethyldisiloxane and are substantially free of other organic and inorganic compounds. The ratio of linear to cyclic polymers in the fluids of the present invention can vary widely but are typically in the range of from about 1:10 to about 10:1.
The present invention also provides a novel method for producing the high isomeric purity poly(3-aminopropylmethylsiloxanes) of the present invention, the process comprising (a) mixing 3-(3-aminopropyl)heptamethyltrisiloxane with a basic catalyst, (b) heating the mixture to produce the homopolymers of the present invention and hexamethyldisiloxane and volatilizing the hexamethyldisiloxane out of the mixture, (c) evacuating the mixture to remove residual hexamethyldisiloxane, and (d) heating the evacuated product to thermally decompose the basic catalyst and recovering the high isomeric purity poly(3-aminopropylmethylsiloxane) homopolymer product.
Preferably the 3-(3-aminopropyl)heptamethyltrisiloxane is 3-(3-aminopropyl)-1,1,1,3,5,5,5-heptamethyltrisiloxane of at least 95% isomeric purity, which is preferably prepared according to the instructions set forth in U.S. Pat. No. 5,892,084.
The basic catalysts useful in the practice of the present invention include most metal hydroxides, metal oxides, quaternary organoammonium hydroxides, quaternary organo-phosphonium hydroxides, and metal trimethylsilanolates. The preferred catalysts are quaternary organoammonium hydroxides, quaternary organophosphonium hydroxides, and metal trimethyl-silanolates. A particularly useful catalyst for the detrimethylsilylation and polymerization of the present invention is tetramethylammonium hydroxide. The catalyst is typically employed in a concentration ranging from about 100 ppm to about 10,000 ppm, preferably from about 1,000 ppm to about 5,000 ppm, and most preferably from about 2,000 to about 4,000 ppm, based on the weight of the 3-(3-aminopropyl)heptamethyltrisiloxane.
The polymerization step (b), which proceeds by elimination of hexamethyldisiloxane from 3-(3-aminopropyl)-1,1,1,3,5,5,5-heptamethyltrisiloxane, of at least 95% isomeric purity, can be carried out at temperatures ranging from about 80xc2x0 C. to about 200xc2x0 C., preferably from about 80xc2x0 C. to about 150xc2x0 C., and more preferably between about 100xc2x0 C. and about 130xc2x0 C. Preferably the heating of the mixture should continue until no further hexamethyldisiloxane is observed to be volatilizing from the residual mixture.
The product of the polymerization/volatilization step (b) is then subjected to evacuation to remove dissolved residual hexamethyldisiloxane. This step is effected by reducing the pressure of the polymerized product to a pressure of about 200 mm Hg, or other pressures as will be apparent to those of ordinary skill in the art.
The evacuated mixture comprising the homopolymers of the present invention and the catalyst are then heated to a temperature in the range of from about 130xc2x0 C. to about 160xc2x0 C. for at least about 2 hours in order to decompose the catalyst, and to drive off the catalyst decomposition products. In this manner, homopolymers of the present invention are formed which are at least about 97% free of hexamethyldisiloxane and which are substantially free, i.e., 98% or more, of other organic and inorganic compounds.
The present invention also contemplates the vacuum distillation of the homopolymers of the present invention in order to isolate the individual homopolymer components or mixtures thereof, such as to isolate the cyclic polymers, including the isolation of (H2NCH2CH2CH2MeSiO)3.